As processor capabilities have expanded and power requirements have decreased there has been an ongoing explosion of devices that operate completely independent of wires or power cords. These “untethered” devices range from cell phones, and wireless keyboards to building sensors and active RFID tags.
Engineers and designers of these untethered devices continue to have to deal with the limitations of portable power sources, primarily batteries as the key design parameter. While performance of processors and portable devices have been doubling every 18-24 months driven by Moore's law, battery technology in terms of capacity has only been growing at measly 6% per year. Even with power conscious designs and the latest in battery technology, many devices do not provide the lifetime cost and maintenance requirements for applications that require a large number of untethered devices such as logistics, and building automation. Today's devices that need two-way communication require scheduled maintenance every three to 18 months to replace or recharge the device's power source (typically a battery). One-way devices simply broadcasting their status (one-way) such as automated utility meter readers have a better battery life, typically requiring replacement within 10 years. For both device types, scheduled power-source maintenance is costly and disruptive to the entire system that a device is intended to monitor and/or control. Unscheduled maintenance trips are even more costly and disruptive. On a macro level, the relatively high cost associated with the internal battery also reduces the practical, or economically viable, number of devices that can be deployed.
The ideal solution to the power problem for untethered devices is a device or system that can collect and harness sufficient energy from the external environment. The harnessed energy would then either directly power an untethered device or augment a battery or other storage component. Directly powering an untethered device enables the device to be constructed without the need for a battery. Augmenting a storage component could be along two lines: 1) increasing the overall life of the device or 2) by providing more power to the device to increase the functionality of the device. The other parameters for an ideal solution is that the harnessing device could be used in a wide range of environments including harsh and sealed environments (e.g. nuclear reactors), would be inexpensive to produce, would be safe for humans, and would have a minimal effect on the basic size, weight and other physical characteristics of the untethered device.